systemd: record the timestamps as early as possible

The time for systemd initialization and selinux policy loading
is accounted to the initrd or the kernel, which is wrong.

Instead of:

Startup finished in 5.559s (firmware) + 36ms (loader) + 665ms (kernel) +
975ms (initrd) + 1.410s (userspace) = 8.647s

the more correct output is:

Startup finished in 5.559s (firmware) + 36ms (loader) + 665ms (kernel) +
475ms (initrd) + 1.910s (userspace) = 8.647s